This invention relates to an industrial robot, and more particularly to a type thereof adapted to be used for assembling various parts.
Industrial robots of cartesian coordinate type, cylindrical coordinate type, and of an articulated type swingable around a plurality of perpendicularly disposed axes have been widely known. Among these types of robots, the articulated robot swingable around a plurality of axes as shown in FIG. 1 is advantageous for assembling parts because of its wide operation range. However, in the situation where a workpiece, with which various parts are to be assembled, is conveyed to an assembling position of the robot by a conveyor and devices for supplying the parts are arranged around the assembling position, only a small part as indicated by two dot dash line in FIG. 1 is utilized within the entire spherical operating range because of the necessity of reducing working time and economizing conveying distance for assembling the robot.
Furthermore, since the workpiece conveyed by the conveyor and the supplying devices for supplying parts cannot be arranged underneath the robot, the number of the parts assembled by the robot is restricted. In addition, because of the posture of the wrist of the robot, assembling operations thereof from a side remote from the base of the robot has been found to be difficult.
For obviating these difficulties, a polar-coordinate robot of a suspending type as shown in FIG. 2 has been proposed in the 14th International Symposium on Industrial Robots held in 1984. in this type of robot, the workpiece to be assembled with various parts is placed below the arm 1 of the robot, and the devices for supplying the parts can be arranged around the workpiece. Thus the operation range S shown in FIG. 2 can be utilized efficiently and the workpiece can be accessed from all the directions around the workpiece.
However, since the arm 1 of this type robot is moved upwardly and downwardly, an excessive space is required above the robot. Furthermore, the wrist 2 of the robot is brought into a desired position by rotating the arm 1 for an angle .alpha., rotating a member supporting the wrist 2 for an angle .beta. around an axis perpendicular to the rotation of the arm 1 and then rotating the wrist 2 for an angle .gamma. around an axis perpendicular to the rotation of the member as shown in FIG. 3(a). Thus, after the parts a, b, c, . . . , f have been transported from the parts supplying devices and assembled onto the workpiece as shown in FIG. 3(b), the arm must be rotated in the reverse direction around its axis for avoiding the rotation of the arm in excess of the limiting angle. Thus, the posture variation of the wrist in the case of assembling the parts cannot be executed at a minimum value of the rotating angle .alpha., and the time required for assembling the parts is increased. In addition, for the purpose of improving the operating speed of the robot, the unbalanced condition in the mass of the arm 1 must be reduced as well as the reduction of the moment of inertia of the arm 1.